Helpers at the nest refers to a situation in which offspring don't leave the parental environment immediately to raise offspring of their own, but remain with the parents for some period of time and assist the parents in raising additional broods.
Waiting to reproduce may be beneficial for birds whose probability of reproductive success is low. Suppose, for example, that reproductive success is limited by the number of available territories in which pairs of birds can breed. A younger, less-experienced bird may not be able to get and hold any territory;
therefore, on his own, he won't have much opportunity for reproduction. If he stays at the parental nest and helps care for his younger siblings, however, he can boost his inclusive fitness.
The reason bird studies tend to focus on the behavior of males rather than females is because it's usually males that defend territories and females that disperse to find mates — you know, the male bird sits and sings and hopes a female flies by. When territories are scarce, extra males pile up around home. In addition, the fact that the females are on the move can also mean increased female mortality, which skews the sex ratio of males to females.
Sometimes, no evidence exists that the helpers at the nest increase the number of offspring the parents are able to raise. In these cases, selection favors helping for different reasons:
1 To gain experience: A wealth of evidence shows that inexperienced pairs of birds are much less successful at raising offspring than are experienced birds. By sticking around to help, the young birds gain experience in parenting.
1 To inherit the territory: In an environment where territories are both limited and needed to successfully raise offspring, staying in the parents' territory may result in a better chance of inheriting the territory when the parents die. (Consider this the suck-up principle.)
1 To wait out tough times: Environments fluctuate, and sometimes there just isn't enough food or enough available mates. In this case, hanging around in a bad year may increase your chance of surviving to breed in a good one later. Got a 30-year-old child living at home? Then you're intimately familiar with this scenario.
The young bird isn't sticking around just to be helpful; he's looking out for himself. The fact that his parents or siblings may benefit from his presence is beside the point. For that matter, the parents aren't acting altruistically either. Even if having the young bird around doesn't increase their own number of offspring, the parents still benefit if, by delaying leaving home, the young bird can increase his own reproductive success.
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